The present invention relates generally to grain drying equipment and more particularly to an improved continuous crossflow column grain dryer with optimum drying air recirculation and simultaneous improved specific grain mass position rotation within the grain column.
It is generally believed that continuous crossflow dryers, that is, those dryers which have wet grain continually entering the dryer and dried grain continually exiting the dryer with drying air passing across the flowing column of grain, were not suitable for drying grains having a high moisture content. The reason for the difficulties experienced in the use of conventional continuous crossflow dryers was that they only operated at their optimum design performance over a fairly narrow band of moisture removal range due to fixed design conditions such as a fixed cooling air flow, a fixed cooling plenum exhaust area, a fixed heated air flow, a fixed heat plenum exhaust area, and homogeneous grain flow with constant exposure of one face of the grain mass to the heat plenum wall, causing heat damage.
At a grain moisture removal of 6 to 8 percentage points, most conventional dryers work satisfactorily. The cooling rate is matched fairly well with the drying rate. The grain column is usually split 25-35 percent cooling and 65-75 percent heating. The total blower horsepower is normally split to be 30-40 percent cooling and 60-70 percent drying. Dryers with a 25 percent cooling column usually use the upper extreme in cooling horsepower, thus operating the cooling plenum at a higher static pressure than the heating plenum and delivering 50-100 percent more cool air per bushel than drying air.
Under conditions wherein grain coming from the field is very high in moisture, and the drying rate is slowed significantly, the grain in such prior art systems was over cooled, which is not a particular problem from the standpoint of the quality of the grain dried, but it does waste considerable energy. Under very dry grain inlet conditions wherein the moisture removal is in the 3-5 percentage range, cooling is inadequate and fuel cost per bushel is very high. If grain conditioned by such a process is to be stored in a non-areated storage and therefore has to be cooled considerably after being dried in the dryer, the only reasonable solution was believed to be to cut back on the drying temperature to drastically slow down the drying rate to the point at which the grain retention time in the cooling zone was adequate to cool the grain. It is well-known that the efficiency of the drying process is reduced when plenum temperature of a crossflow dryer is reduced. It is also well-known that the grain to be stored in non-areated storage cannot be too hot or it will deteriorate. There is, therefore, the need for a continuous flow drying apparatus which will overcome these problems found with prior art devices.
Another weakness with most conventional continuous crossflow column grain drying devices is that when drying grains under conditions where cooling the grain in the dryer is not desired, the cooling air flow must be blocked off and the cooling grain column is of little or no value in drying. There is, therefore, a need for equipment of this type which will adequately compensate for this situation by having a design that can be easily adjusted to provide drying of grain in the grain column area normally used for cooling to maximize the performance of the dryer.
It is also known that conventional continuous flow column grain drying devices are limited in their maximum plenum temperatures and therefore in their drying efficiency because of the kernel temperature limits of the layer of grain that is continuously exposed to the hot plenum air as the grain moves downward sliding against the inner perforated grain column wall that forms the plenum chamber walls. There is, therefore, a need for equipment of this type which will overcome this kernel temperature limitation and improve drying efficiency by proving a design that limits the amount of travel that a given layer of grain can move in direct contact with the heat plenum wall before it is positively displaced by a cooler, wetter layer of grain, with this process alternating between (but not limited to any given sequence of full and partial column width changes) partial thickness changes and full thickness changes so that a given grain kernel would have little or no opportunity of repeating its contact with the hot plenum wall.